Containers utilizing propellants to discharge their contents have enjoyed widespread popularity over the years since they are extremely compact and portable, inexpensive and simple to operate, and capable of serving as product storage containers when not in use. Such pressurized product containers include both those of the aerosol-type, in which the propellant and product are mixed before being expelled through the container's discharge valve in atomized form, and the so-called "barrier pack" canisters or cans, in which the product is contained in a collapsible inner product bag packaged inside an outer can, with a pressure generating propellant disposed between the two. When the barrier pack discharge valve, which is connected to the inner bag, is opened, the packaged product is discharged through the valve, as a result of the pressure from the propellant acting against the outside of the inner bag, resulting in the latter's compression.
In instances where the entrainment of propellant in the product to be dispensed must be avoided, the barrier pack has distinct advantages over the aerosol containers, due to the isolation of the propellant from the product. A further advantage is to be found in the fact that the propellant is prevented from escaping to the atmosphere during discharge of the product, thus avoiding potential safety hazards, as well as environmental problems.
A variety of inner containers have been proposed for barrier packs, for example, a pleated bellows-like container that collapses along its longitudinal axis, forcing the product through an opened discharge valve. A drawback of the container, however, is its tendency to trap air in the extremities of the bellow folds during the product filling operation, particularly evident in the case of viscous products. With time, the trapped air migrates throughout the interior of the container in the form of bubbles which contaminate the product. As suggested this can be undesirable, for example, in the case of room temperature vulcanizing silicone products intended for the formation of gasketing material. The entrapped air tends to destroy the sealing integrity of gaskets formed from such product, making the container unsuitable for the application.
Another approach proposed involves the use of the so-called piston-type barrier pack can in which a movable partition disposed transversely across the can's cross-sectional area provides a barrier between the product in the upper part of the can, and the propellant located in the bottom thereof. When the discharge valve is open, the propellant forces the partition upwardly in the can, resulting in the expulsion of product through the valve. Unfortunately, while effectively isolating the propellant from the product, injury to the can, for example dents therein, interfere with movement of the partition, disabling the discharge process.
Still another solution proposed has involvd the use of a flat-bottomed, cylindrically-shaped inner container formed from thin-walled plastic that is inserted in the outer pressure can by forcing it through the relatively constricted upper opening in the can's top. The inner container is thereafter collapsed by the propellant's pressure when the valve attached to the container is opened, resulting in the discharge of the container's contents. However, the process of forcing the container through the constricted opening results in permanent indentation of the inner container, producing distortions which are permanently set into the walls of the container that prevent its proper filling. Furthermore, the flattened bottom of the inner container can act in a fashion similar to that of a reinforcing element. This interferes with the total collapse of the container, trapping product therein which becomes unusable as a consequence. In addition, the right angle interface of the container's flat bottom with its vertical walls has a tendency to retain air adjacent thereto during the filling process, again resulting in the undesirable contamination previously described.
A somewhat different approach, but like that involving the plastic flat-bottomed cylindrical container, makes use of a similarly shaped container which, however, is fabricated from thin walled aluminum, rather than plastic. While such a container avoids permanently set indentations, and tends to collapse more completely than the plastic container described, it still suffers from a tendency to trap air at the junction of the container's flat-bottom and its wall, again resulting in undesirable air contamination of the product. In addition, the manufacture of thin-walled aluminum containers requires relatively complex machinery, and the containers are expensive to fabricate.